(Q). How many natural numbers less than 1000 will have exactly 3 factors?
Solution:-
Only square of a prime number has three factors, So the number are:
2², 3², 5², 7², 11², 13², 17², 19², 23², 29², 31²
above numbers are less than 1000 & each one has 3 factors
Hence there are 11 desired numbers. Answer
